The invention is directed to a gasification reactor comprising a pressure shell, a reaction zone partly bounded by a vertically oriented tubular membrane wall, a horizontally directed burner having a burner head at which, in use, a combustion flame is discharged into said reaction zone, said burner protruding into the vertical wall part of the membrane wall via a burner muffle.
Such a gasification reactor is described in U.S. Pat. No. 4,202,672. This publication describes a coal gasification reactor provided with a pressure shell, a reaction zone and a membrane wall, which partly defines the reaction zone. The tubular shaped membrane wall comprises interconnected conduits in which evaporating cooling water is present.
In U.S. Pat. No. 4,959,080 a coal gasification process is described which may be performed in a gasification reactor as above. This publication describes that a layer of slag will form on the membrane wall during gasification of coal. This layer of slag will flow downwards along the inner side of the membrane wall.
The Shell Coal Gasification Process also makes use of a gasification reactor comprising a pressure shell and a membrane walled reaction zone according to “Gasification” by Christofer Higman and Maarten van der Burgt, 2003, Elsevier Science, Burlington Mass., pages 118-120. According to this publication the Shell Coal Gasification Process is typically performed at 1500° C. and at a pressure of between 30 and 40 bar. The horizontal burners are placed in small niches according to this publication.
Applicants have successfully performed the Shell Coal Gasification Process at the lower end of the above disclosed pressure range. It is however desirable to operate a gasification reactor at higher pressures because, for example, the size of the reactor (diameter and/or length) can then be reduced while achieving the same capacity. A reduced diameter of the gasification reactor provides a smaller circumferential area for the slag running down the vertical membrane wall. At an equal reactor throughput the thickness of the fluid slag layer is increased thereby. This effect is even bigger by using high-ash feedstocks. It has been found that with increasing gas pressures and reduced reactor diameter, slag ingresses into the burner muffles. This slag deflects the oxygen/coal flame towards the metallic muffle walls, which causes extremely high heat fluxes. In combination with the higher overall surface temperatures steam blankets can be formed on the water cooling side, resulting in that locally no adequate cooling exists. This in turn may result in that at such locations the metal of the membrane wall melts away.
U.S. Pat. No. 4,818,252 describes a burner muffle as present in a membrane wall of a gasification reactor. The burner muffle itself can be adapted in design depending on the gasification conditions. The design comprises a vertical cooled shield comprised of interconnected concentric tubes around an opening for a gasification burner. This vertical concentric shield can be placed at different horizontal positions, i.e. closer to or further away from the membrane wall.
The burner muffle of U.S. Pat. No. 4,818,252 is however vulnerable to slag ingress, when the gasification reaction is conducted under conditions wherein a thick layer of viscous liquid slag forms on the inside of the membrane wall. In such a situation the slag will flow in front of the burner head and disturb the combustion. U.S. Pat. No. 4,818,252 discloses a slag deflector in FIG. 14 to avoid that slag covers the burner head. However, this design is not adequate to cope with thick layers of slag.
It would therefore be an advancement in the art to provide a gasification reactor as described above, which can operate at the higher pressures and which can either avoid the large heat fluxes or alternatively at least minimize the adverse consequences of such heat fluxes. It would be a further advancement to provide a gasification reactor, which can operate at high slagging conditions.